1. Field of the Invention
The present invention relates to package systems that include a peelable seal, and in particular, the present invention relates to compositions and methods for forming such peelable seals.
2. Background Art
Packaging is an important feature in selling and marketing most products. Food products, in particular, have rather stringent packaging requirements in order to preserve freshness and enhance shelf life. Certain medical devices also present strict packaging requirements in order to preserve sterility of such devices. In such applications, the package is typically vacuum-packed or gas-flushed and subsequently hermetically sealed. Although efficient packaging of products is mandatory, various aesthetic properties of a product package are also important. For example, the appearance of a product is important in appealing to consumers. Moreover, in many applications and, in particular, for food products reusability and ease of opening of a package are also important considerations. In many applications, the ability to easily open a package will depend on the mechanical properties of the seal.
One particularly important packaging structure utilizes a peelable seal. In at least one prior art packaging system, a peelable seal is formed by coating a heat sealable polymeric material onto a metal foil. Since packaging incorporating such seals are often impervious to air and contaminants, peelable seals must also be impervious to these materials. When a package having a peelable seal is opened, a sealing layer may be peeled away from a substrate. It is desirable for such peeling to be achievable with a low and relatively constant peel force. The elastic properties of the peelable seal are such that failure of the seal does not occur from flexing and normal handling of the package. In some prior art packaging, peelable seals are constructed from multi-layered sheets. Examples of packaging systems having such seals include tray-type food packages, bottles or blister packages, and the like. Although some of the prior art peelable sealing packages work reasonably well, it has been difficult to construct packaging systems that consistently form hermetic seals that resist leaking while being easily opened by an end user. Moreover, such prior art peelable packaging systems tend to operate over relatively narrow ranges, and in particular narrow temperature ranges. Narrow sealing temperature ranges tend to result in packaging defects. For example, on the low end of the usable temperature range leaking seals may be formed (not hermetically sealed). On the high end of the usable temperature range, non-peelable seal are formed which tear when opened.
Accordingly, there exists a need for improved peelable packaging systems that resist leaking, provide a hermetic seal, and open easily.